Long-range goals: to investigate the control of renin and aldosterone secretion in relation to circulation and kidney function. Effects of bed-rest, posture and electrolyte balance will be compared in normal controls and circulatory disorders, especially hypertension. Proposed methods: Under controlled conditions, to measure and evaluate factors believed to control renin release (arterial and intrarenal pressures, electrolyte balance, and adrenergic nerve activity); to relate these stimuli to plasma renin, aldosterone, and norepinephrine levels; and by using appropriate blocking agents, to estimate the effects of circulating pressor factors on the general circulation (cardiac output, peripheral resistance, and central blood volume) and on regional circulation. Collaboration with the Cardiology Division is on- going, reflecting a common interest in control of circulation. Computer simulation will assist in evaluation of results.